Fastned recently released a very interesting article with basics on electric car charging and particularly fast charging.
The article starts with a general explanation of battery charging - always by direct current (DC), which means that when using AC charging stations, the current is rectified using an on-board charging system. The DC charging (directly from the fast charger) bypasses the on-board charger and the current goes right to the battery.
The on-board charger is usually low-power (several kW, sometimes in the range of 11-22 kW, three phase).
AC and DC fast charging is different (Source: Fastned)
The capability of DC fast charging depends on the capabilities of the infrastructure (charger power, voltage and current) and car (battery type and size, temperature and more).
Typically, higher capacity battery packs (like 100 kWh and up) can take higher power than smaller ones (like 24 kWh), especially if they area similar type. Because charging generates heat, charging speed could be significantly affected if there is no temperature management system. Charging becomes slow if the temperature is very low (below 0°C) or the state of charge is high (above 80% or 90%) too.
Most of the electric cars can take less than 50 kW of power even if the charger is able to supply more. Some exceptions are Tesla cars (up to 130 kW) or the Hyundai IONIQ Electric (up to 70 kW). Fastned already installed several 175 kW DC fast chargers and found out that those chargers enable a shortened time of IONIQ charging by up to 50%.
In the future, charging stations will have higher power and electric cars are expected to accept higher power charging, which will translate to higher speed of replenishing range.
Increasing range added per 20 minutes of charging (Source: Fastned)
Fastned also shared its result about when the fast charging take place most often. As it turns out - between 10 AM and 8 PM, which means that solar generation would be a perfect patch for the stations.
Distribution of fast charging sessions throughout the day (24 hours). (Source: Fastned)
And finally, it's interesting how Fastned sees its business future - the charging stations are to be scaled up in terms of power (175 kW and then 350 kW) and the number of chargers, so dispensed electricity and revenues will reach a lot higher levels:
Fastned fast charging station
"Stations with two typical 50 kW fast chargers can provide a — conservatively estimated — maximum of 560 kWh per day. This enables 2.800 km electric kilometers per day. I base this on the historical data we already have on fast charging behaviour of our customers:
- Fast charging stations are mostly used between 07:00 and 23:00 — 16 hours of use per day.
- A maximum of 50% utilisation during the hours of use (half of the chargers are in use during these 16 hours).
- On average an EV charges at 70% of the maximum that a fast charger can provide (not all EVs will be able to charge at full speed for the entire charge session).
In the coming years, more vehicles become capable of charging with high speeds. With more powerful chargers a single station can serve more vehicles. Now let’s see what happens when we upgrade a 2x 50 kW station to 4x 175 kW or to 8x 175 kW:"
Capacity of fast charging stations (Source: Fastned)
"An existing station has a capacity of 204.000 kWh annually and an upgraded station more than 1.4 million kWh. A next generation station thus provides 7X more capacity on the same land area, and 14X more capacity with 8 chargers. That’s an order of magnitude improvement.
The economics of faster charging stations The capacity of a station 2.0 is seven to fourteen times that of a current fast charging station. However, the one-off costs (CAPEX) such as permits, grid connection, equipment, construction, installation and project management of a station equipped with four 175 kW chargers are far below that of constructing six to thirteen additional stations. Recurring costs (OPEX) such as technical maintenance and cleaning are only slightly higher for the 2.0 station. Capacity thus rises (much) faster than costs do. Therefore the cost per kWh delivered decrease (as long as a station has a certain number of customers per day).
Another advantage lies in maximizing the use of a single grid connection. In many countries electricity prices are heavily taxed. Many of these taxes are regressive: the more you consume per grid connection, the less taxes you pay per kWh.
Can the grid handle this? As long as fast charging stations are connected to medium voltage rings (10kV or 20kV), station power can be scaled up in line with the expected exponential take-off of electric vehicles. Supermarkets, high rise office buildings and large warehouses are routinely connected to the medium voltage grid with connections of 1 or 2 MW. Fast charging stations are comparable in power draw and are well within the limits of the capacity of the medium voltage grid."